Vacuum bag for forming fiber reinforced composite articles and method for using same

ABSTRACT

An vacuum bag for forming of a fiber reinforced composite article, made of a curable elastomer, having molded in resin distribution means. Optional vacuum conduits are molded into the periphery of the bag, causing the bag to be adapted to any number of mold shapes. The bag contains a resin distribution conduit sealed into the vacuum bag. A multiplicity of cross channels are formed on the inner surface of the bag, covering most of the area under which the fiber lay up is placed within the mold. These cross channels can be formed from a pattern of multiple, variegated small dots or pentagons, which, under vacuum, leave a multiplicity of small crisscross channels running along the inner surface of the vacuum bag. This pattern of distribution channels covers most of the fiber lay up, except for a perimeter area which insures resin flow into rather than across the fiber lay up.

RELATED APPLICATIONS

This Application is a continuation of application Ser. No. 08/465,230,filed Jun. 5, 1995, now U.S. Pat. No. 5,601,852, which is a continuationof application Ser. No. 08/250,169, filed May 27, 1994, now issued asU.S. Pat. No. 5,439,635, which is a continuation-in-part of applicationSer. No. 08/018,827, filed Feb. 18, 1993, now issued as U.S. Pat. No.5,316,462.

BACKGROUND OF THE INVENTION

This invention relates to transfer molding techniques for the productionof fiber reinforced resin composite structures. In particular, itrelates to processes and apparatus for molded, vacuum bag constructionof fiber reinforced resin composite structures of various shapes.

Fiber reinforced resin composite structures have taken many shapes andforms, including tubes or conduits as employed in the chemicalprocessing industry, flat sheets and compound shapes as employed in boatbuilding and extensive curved shapes as employed in aerospace. In theseconstructions a fiber reinforcement is laid up against a mold to providethe desired shape. This fiber reinforcement may be prewetted with resin,forming a "pre-preg" structure. More often a dry lay up of fiber isplaced upon a mold and then wetted through by resin. The resin isallowed to set and cure upon the mold to form the fiber reinforced resincomposite structure. Critical problems involved in this process includethe uniform distribution of resin into the fiber, the elimination of airvoids and bubbles,elimination of areas not wetted by resin within thefiber structure, and reduction of the use of excess resin or waste ofresin in the process. The apparatus and processes, used to make thesestructures therefore vary considerably depending upon the specific shapeand form of the structure to be produced.

A common technique is the so called vacuum bag technique which has beenused to form fiber reinforced plastic structures. In vacuum bagtechniques, flexible sheets, liners or bags are used to cover a moldwhich contains the dry or wet fiber lay up. The edges of the flexiblesheet are clamped or sealed against the mold to form a sealed envelopesurrounding the lay up. A catalyzed liquid plastic or resin isintroduced into the envelope, into the interior of the bag, to wet thefiber, and a vacuum is applied to the bag interior via a vacuum line tocollapse the flexible sheet against the fiber and surface of the mold.The vacuum serves to shape the article to the mold, to draw the resinthrough the fiber mat, completely wetting the fiber, and to remove anyair which would form voids within the completed article.

The vacuum is continued while the plastic wetted fiber is pressed andcured against the mold to form the desired shaped fiber reinforcedplastic structure. Since the entire resin curing process occurs within asealed bag, and a continuous application of vacuum draws off all fumesthrough filters, resin fumes from the process are prevented fromescaping into the ambient work space.

My prior U.S. Pat. No. 5,052,906 and U.S. Pat. No. 4,902,215 disclosevacuum bag structures in which distribution media are placed within thevacuum bag, surrounding the fiber lay up, in order to enhance theuniform distribution of resin through the composite upon the applicationof a vacuum. In order to enhance the separation of the completed moldedfiber reinforced plastic structure from the mold and the bag, and toreduce the chances of contamination of the surface of the structure,peel plies, in the form of porous thin sheets which do not adhere toresin, are provided between the distribution media and the fiber lay up.

In the cited patents, fiberglass reinforced laminates are shown thathave very desirable resin to fiber ratios and uniform mechanicalproperties. The vacuum bag process produces high strength structures invery complex shapes including boat hulls. However, each article createdin this manner requires a separate set up of vacuum bag and distributionmedia; while this is desirable for one of a kind production, it is notthe most efficient method of molding repeated identical structures.

In early vacuum bag structures, such as British Patent No. 944,955, thereinforced fiber structure is laid upon a single cavity mold, the moldcovered by a flexible sheet or vacuum bag and the outer edges of thesheet sealed upon the mold to leave a space containing the dry fiber layup. The liquid resin is introduced via supply line located at the topcenter of the bag and the vacuum is drawn on the bag by a vacuum linelocated at a peripheral edge of the mold. The collapse of the bag underthe vacuum presses and forces the resin and fiber against the contour ofthe mold. A viscous resin require squeezing or rolling to distribute theresin through the fiber.

Other patents have suggested channels to distribute the resin throughthe fiber including U.S. Pat. No. 4,312,829 to Fourcher and U.S. Pat.No. 2,913,036 to Smith.

In U.S. Pat. No. 4,942,013 to Palmer, et al. a structure is shown inwhich the resin is introduced through an opening at one end of the moldand a vacuum is drawn from the other end of the mold, thus drawing theresin laterally across and then through the fiber lay up. A secondfiberglass layer is required to aid in the distribution of the resin.

SUMMARY OF THE INVENTION

This invention is the formation of a vacuum bag, preferably of siliconerubber, having molded therein a resin distribution means formed to thespecific article to be made. Alternatively, vacuum conduits can also beprovided at the periphery of the bag, causing the bag to be adapted toany number of mold shapes without requiring vacuum conduits to be placedin the mold. The inventive bag may be constructed as a unitary articleupon the base mold which forms the base for the construction of thedesired fiber reinforced plastic article. The bag may be alternatelyformed from connected, preformed sheets, each of which contains moldedin resin distribution channels.

The article contains an open sided, resilient main distribution conduitrunning laterally along the long axes of the desired vacuum bag withbranch conduits, depending upon the shape of the mold, to provide forlong distance flow of resin to all parts of the article to be made. Amultiplicity of cross channels are then formed on the inner surface ofthe bag, covering most of the area in which the fiber lay up is placedwithin the mold. These cross channels can be formed from a pattern ofmultiple, variegated small dots, pillars, cones, or pyramid shapestructures, which, under vacuum, leave a multiplicity of small channelsto run along the inner surface of the silicone rubber vacuum bag. Thispattern of distribution channels covers most of the fiber lay up, exceptfor a perimeter area which is left without channels to insure resin flowinto rather than across the fiber lay up. Optionally, along theperiphery of the vacuum bag, outside the area of the fiber lay up, is acontinuous circumferential, non-collapsing vacuum outlet conduit.

Each of the major vacuum and resin conduits is provided with an inlettube connection formed of an elongated thickened wall opening into whicha vacuum tube or resin supply tube may be inserted and which is amenableto being sealed with a tacky tape or similar seal. This permits theresin introduction and vacuum draw to be through standard thick walledplastic tubing which can be inserted into the bag without the necessityof connectors.

The bag is sealed against the mold using appropriate tacky tape edgeseals, although in some circumstances the bag itself has sufficientadhesion to be sealable.

The bag is most suitable for the repeated manufacture of a number ofidentical fiber reinforced plastic articles. The base mold can be usedas structure upon which the vacuum bag is built. Either a wax lay up oran actual article covered with suitable separating materials can be laidup upon the mold and covered with a peel sheet. A resin distributionmedium can then be laid over the peel sheet. This medium is then coveredwith a flexible open rod or tube running along the desired location ofthe resin distribution channels and the vacuum receiving channels. Thisset up is then sprayed or coated with a separation compound.

The vacuum bag of the invention is created by applying a viscoussilicone rubber compound in multiple coats over the completed lay up,building the bag up to a suitable thickness. The silicone rubber is thencured and peeled away from the distribution medium and the positivetubing. The resulting silicone rubber structure contains an integralresin distribution medium and vacuum channels adapted to vacuum formingof the article. It may be readily reused as a vacuum bag for therepeated manufacture of fiber reinforced articles.

In the use of the inventive vacuum bag it is necessary only to lay up adry fiber preform against the mold in the desired orientation andthickness. A peel layer or peel sheet may be applied over the fiber. Theinventive silicone rubber vacuum bag is placed over the peel sheet andfiber, and sealed to the mold. A vacuum is applied and then resinintroduced until resin runoff within the vacuum channels indicates totalimpregnation of the article. The article then is allowed to set untilthe resin cures.

The bag may then be readily peeled from the article, cleaned of anyresidual resin and reused.

As can be seen, once such a bag is made for a specific article, it canbe reused without the necessity of laying up individual distributionmedia and channel structures for each repeated construction of copies ofthe fiber reinforced article.

It is accordingly the primary object of the invention to disclose auniform vacuum bag structure which can be readily manufactured for aparticular article and mold, and which integrates the features of resindistribution and vacuum draw off with the sealing and pressing featuresof a standard vacuum bag.

It is the further object of the invention to disclose a vacuum bag whichis conformably formed to provide the most uniform possible pressurestructure for the manufacture of a fiber reinforced composite structureagainst a mold.

It is the further object of the invention to disclose a vacuum bag whichassures uniform resin distribution throughout the fiber lay up for avacuum bag molded fiber reinforced composite structure.

It is the further object of the invention to disclose a vacuum bag whichmay be rapidly reused for the rapid production of a series of identicalfiber reinforced composite structures on a mold.

It is the further object of the invention to disclose a process forcreating a vacuum bag adapted to a particular mold and a particulardesired composite structure, for rapid, accurate, and repeatableproduction of multiple copies of the fiber reinforced compositestructure.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 is a side view of a fiber lay up using the invention.

FIG. 2 is a top view of an embodiment of the invention.

FIG. 3 is a sectional view of the invention, including a view of aconduit.

FIG. 4 is a cut away view of a second embodiment of the invention.

FIG. 5 is a face view of a pattern mask.

FIG. 6 is a section through FIG. 5.

FIG. 7 is a section view showing formation of a sheet of the invention.

FIG. 8 is a section through a sheet of the invention.

DETAILED DESCRIPTION OF THE INVENTION

The invention is best shown in comparison to my prior U.S. Pat. No.4,902,215, incorporated herein by reference in full. In side view inFIG. 1, I show a dry lay up for manufacture of a fiber compositestructure 1, utilizing the inventive vacuum bag 4.

The composite 1 is formed on a rigid mold 6, for this illustrativepurpose a flat smooth table surface forming a backing for the fibercomposite article 1. A pattern of dry reinforcing fibers 2, such asfiberglass or carbon fibers, is laid on the mold 6. The shape of themold 6 determines the shape of the final structure 1, and thus the mold6 can be curved or of any desired shape, as will be illustrated below.

In the prior art, a peel sheet 3 would be placed over the fiber lay up2, and then a distribution layer laid on the peel sheet to enhance flowof resin to impregnate the lay up 2. A resin entrance chamber would becentrally placed on the lay up with a communicating resin distributionchamber to communicate resin flow to the distribution layer. A vacuumoutlet, either in the rigid mold or on the outer periphery of the layup, would communicate with a source of vacuum. A vacuum bag or sheetwould then be placed over the entire assembled lay up and distributionlayers, and sealed around its perimeter to the mold. A vacuum, appliedto the vacuum outlet, would draw the vacuum bag against the lay up. Thevacuum both draws the resin throughout the fiber lay up, and presses theresin impregnated lay up against the rigid mold to smoothly form thedesired fiber reinforced shape.

It should be appreciated that this process requires individual labor toset up the same distribution layers, chambers and vacuum bag in separatesteps, even though identical articles may be desired. There are noeconomies of scale in this process, and every article manufactured ismade as though it were a one of a kind article.

In the invention, a preformed vacuum bag with integral resindistribution piping and distribution pattern, and optional vacuumpiping, is created for the composite article which is to be formed. Tocreate this inventive vacuum bag 4, the desired rigid mold 6 is firstcovered with a model of the desired finished fiber compositestructure 1. This can be a master article, manufactured as stated above,or a wax or wood model, or some combination of fiber composite basearticle and wax or wood additions, to create the external shape of thedesired article 1. This master article pattern is then coated with aseparation layer, such as a 50% soap and water mixture. The separationlayer is allowed to completely dry.

A reverse master resin distribution pattern, of one of the various formsas illustrated in my prior '251 patent FIGS. 3-7, is then applied overthe outer surface of the model article 1. This reverse master patternmay be the mirror image of any pattern of continuous small channels 14,preferable running in two cross wise directions. Such a reverse masterpattern could include a repeated pattern of cylindrical dots, or smallregular polyhedral solids 16. It can also include the pattern of spacedapart rows, crossed by an overlying pattern of spaced rows at rightangles to the first rows.

Over the reverse master pattern is laid a hollow piping structure ofsignificantly greater cross sectional area. Such a structure should runthe long length of the desired article 1, and for a wide or complexshape, preferably has branch conduits so that no part of the article 1is more than forty-eight inches from a conduit.

Optionally a second conduit structure 24 is placed as a continuous ringaround the bag, communicating for vacuum flow from the mold 6, justoutside the perimeter B of the pattern master article 1.

This distribution pattern and the conduit(s) are in turn coated with aseparation layer which is allowed to dry.

The inventive vacuum bag 4 is then formed by repeated applications of anelastomer, such as a viscous, curable silicone rubber, or other peeling,resin resistant curable elastomer, to cover the assembled master pattern1, building up a layer of elastomer with greater thickness over thehollow conduit structures 10, 24. Thicker extensions 19 extendingoutward from these conduit structures may be provided, to extend beyondthe outer limits of the article 1, and to be completely coated withelastomer. The second conduit structure 24 may be reinforced byembedding a helical coil or spring 25 into the vacuum conduit 24 wall toprevent collapse of the conduit 24 upon application of a vacuum from avacuum source 26.

A suitable material for forming vacuum bag 4 is Dow Corning ToolingElastomer THT™. This elastomer is translucent, helping in monitoring theprogress of the construction of the vacuum bag. This material has aviscosity of 450 poise, which helps give good brushability, and cures,when catalyzed, at room temperature within 24 hours.

After cure, the vacuum bag 4 is peeled from the underlying patternarticle 1. The recommended elastomer has high tear strength, reducingthe chance of damage to the finished bag. The bag may be additionallyreinforced by fiber reinforcement, such as nylon fibers, applied as ahand lay up during the construction of the bag.

The conduit sections produce, within the finished bag 4, a pattern ofelongated flow conduits 10 communicating with the inner surface 12 ofthe vacuum bag 4. These flow conduits 10 communicate for fluid flow witha resin distribution pattern 14, formed from the imprint of the reversemaster resin distribution pattern. This pattern 14 will normally be across hatch of small channels at right angles to each other, separatedby a repeated pattern of small bumps 16 on the inner surface of the bag.These bumps 16 may be pyramidal shapes, or spherical, or smallcylindrical or square pillars. Any such repeated pattern of bumps 16that will support the channels 14 against complete collapse under avacuum is suitable, so that the bump pattern will press against thefiber lay up 2 but the channels 14 will remain open a spaced distancefor resin flow.

The bag build up around the piping extensions creates hollow curedelastomeric tube receptacles 20 on the bag exterior, which connect forfluid flow with the interior elongated flow conduits 10 in the innersurface 12 of the bag 4. These tube receptacles 20 accept and seal aninserted plastic tube 22 for connection with a resin dispensing system23, and, where a surrounding vacuum flow conduit 24, with reinforcingwall helical springs 25, has been formed in the bag 4, with tubing 22connected to a vacuum source 26.

The resulting bag 4 is a monolithic vacuum bag structure having embeddedresin conduits 10 and distribution channels 14 which have beencustomized to the article 1 desired to be made on a specific rigid mold6. This inventive bag 4 can therefore be repeatedly used to makeaccurate, identical fiber reinforced articles 1. In each case it isnecessary only to make the fiber lay up 2 against the mold 6, add thepeel layer 3 if desired, and then cover the lay up with the vacuum bag 4of the invention, sealing the bag to the mold with tacky seal 30.

The described material for making the inventive bag 4 does not adhere toresins. This has the advantage that the bag 4 can be easily peeled fromthe composite structure 1 and any residual resin in the distributionchannels 10, 11 formed in the bag 4 may be easily removed. It has thedisadvantage that it is difficult to seal the bag 4 to the mold 6 usingthe tapes of the prior art vacuum bag process. However,those skilled inthe art know of a "tacky tape" which may be used to seal the bag to themold, and Schnee Moorehead Adhesives Part #5601 has been reported to besuitable. Alternatively, a suitable adhering material, such as teflon,may be embedded in the perimeter of the vacuum bag during manufactureand cure, to provide a suitable surface to seal the bag. In somecircumstances, such as where the mold is a planar smooth surface, suchas a metal topped table, the silicone rubber vacuum bag may adhere tothe table sufficiently to provide a suitable seal.

It is recognized that the design of the bag 4 should be such that theresin is distributed from the center of the article A to the peripheryB, and the vacuum should be drawn from the periphery B. This set upserves to purge any air leaks from the seals at the periphery of thevacuum bag preventing air bubbles or voids in the resin impregnatedfiber. This flow arrangement can easily be established by the set up ofthe article master pattern during the construction of the bag 4.

The construction of the bag 4 is otherwise highly variable to meet theshape of the desired article and mold. For example, in my prior patent'215 FIG. 8, a section of the large structure such as a boat hull isshown. In such a structure, the flow of resin is aided by gravity to theperiphery of the bag. If for any reason the mold should be inverted,than several resin inlets could be provided, and resin supplied to eachin turn as the resin flows centrally outward through the reinforcingfiber lay up. The translucency of the vacuum bag is advantageous in thatthe progress of the resin can be visually followed by manufacturingpersonnel so as to sequence the supply of resin.

The vacuum outlet 26 does not have to be molded into the bag. Providingvacuum conduits 24 in the bag 4 may be useful on complicated molds 6, orwhere the mold 6 cannot be provided with an internal vacuum outlet 26and distribution conduit 24. Otherwise the vacuum conduits 24 may be inthe mold 6, and the bag 4, when created, is extended to cover the vacuumconduits 24, the distribution pattern 14 in the bag inner surfacerunning almost to the position of the mold's vacuum conduits.

An alternate form of the inventive bag 4 is formed by providing apolymer film bag having sufficient rigidity to resist collapse underfull vacuum, embossing within the polymer film a master resindistribution pattern to provide the pattern of continuous small channels14 which may run in cross directions or in random directions so as toprovide the desired two dimensional crosswise flow of the resin. In thecase of a rigid polyethylene or plastic bag 4 of this inventive type,the master pattern would primarily comprise a repeated pattern ofgrooves or channels which may be regular or irregular in extent butwhich should extend uniformly across the entire sheet of the rigid bag.Placed within the rigid bag 4 is a hollow piping structure 22 of crosssectional area running the long length of the desired vacuum bag 4,alternately containing branch conduits 10 emanating at right angles froma long conduit. A resin supply 23 opening is provided into at least onepart of the conduit through the rigidified vacuum bag 4.

The rigid conduits 10 provide for supply of resin which is rapidlydistributed under the rigidified plastic sheet under the application ofvacuum. The rigidified plastic sheet is chosen of a material which willconform in general shape to the article being formed but which willmaintain the internal channel structure 10, 14 for the distribution ofresin between the bag 4 and the article being formed even under theapplication of a vacuum to the overall bag 4. Thus the bag forms theresin distribution panel 14 from a cross hatch, which can include arandom cross hatch, of non-collapsing essentially V-shaped channelswhich the stiffness of the bag retains even under the application of avacuum.

A suitable material for forming such a bag is polyethylene sheet. Thismaterial remains sufficiently flexible that it can be rapidly appliedover the fiber lay up of an article by means of tacky tape as describedabove and has the further advantage that it provides for a ready andeven distribution of resin even under a one time use. The chosenmaterial is not adhesive to resin and may easily be pealed from theresin. If desired, a suitable separation layer may applied to theinterface of the material before being laid up against the article to beimpregnated. This alternate form of the bag has the advantage,therefore, that it is suitable for one time as well as repeated use andprovides the integral uniform resin channels without requiring aseparate distribution layer between the outer vacuum bag and the articlebeing laid up.

An alternate form of inventive vacuum bag 4 is formed from a sheet 49 ofuncured vacuum bag material. In the example described herein, thismaterial is an uncured silicone rubber, but any thermo-setting orotherwise curable plastic material can readily be used for the process.A fixed mask 50 for generating a repeated pattern of uniform width resinflow channels 14 is provided.

In the preferred embodiment, mask 50 is a sheet 52 of metal or similarmaterial with a repeated densely packed pattern of polygons 54(preferably hexagons) cut into the sheet. Any regular circle, ovalshape, or polygon 54 capable of being uniformly patterned within a sheet52 would be suitable, and there is additionally no reason why any densepacked tiling of irregular patterns 54 (such as a Penrose tiling) couldnot readily be used. It is desirable that the distance between any resinchannel 14 and the center of its adjoining polygon 54 in the sheet 52 beminimized and it is also desirable that the resin channels 14 be of afairly uniform width so as to prevent uneven concentration of resin inthe finished article. With regular polygons, this is accomplished bymaking the polygon 54 relatively small. A pattern of polygons rangingfrom under one inch across to less than a quarter of an inch across hasbeen found suitable.

It is also suitable that the mask 50 be a cylindrical mask, with thesheet 49 molded into the mask by an embossing roller, or other form ofextruding the sheet 49 into the pattern of the mask 50. Similarly, whilethe preferred embodiment uses a polygonal pattern in the mask 50 forforming the bumps 16 of the vacuum bag 4, a pattern such as denselypacked ovoids (ovals or ovals having more pointed ends), or any otherpattern which produces interwoven channels 14 which promote smooth evenresin flow, may be suitable.

An elastomeric sheet 49 of material from which the vacuum bag 4 is to beformed is laid across this mask 50 and a vacuum drawn on the undersideof the mask 50. An elastomeric sheet 49 may be a thermoplastic,thermoset plastic, silicone rubber, a polyurethene rubber, or othercurable or plastic or elastomeric sheet. All such materials aresettable: they may be deformed into a shape and then set in that shapeto form the bag 4 of the invention. Alternately, pressure may be appliedat the top of the sheet 49 to extrude the sheet 49 into the mask 50forming the repeated pattern of raised bumps 16 on the sheet 49corresponding to the polygonal structure embedded in the mask 50, andforming a series of recesses 14 in the sheet 49 corresponding to thelands 56 between each polygon 54 on the mask 50. The sheet 49 is thencured either by the application of suitable temperature cycling, byexposure to a curing agent or the like. Upon curing, the sheet 49 isthen removed from the mask 50. The result is a vacuum bag sheet 4 havinga uniform pattern of resin channels 14 throughout the sheet extendingacross the face 12 of the sheet, spaced from the base of the sheet byraised bumps 16 corresponding to the polygonal holes 54 within the mask50. It can readily be seen how such sheets 49 can be mass producedrepeatedly by use of the same mask 50.

In use, the vacuum bag 4 is formed by placing repeated sheets 49 overthe article to be vacuum impregnated, which is laid up as a mat orrepeated mats 2 of a fiber-reinforcing material such as fiberglass,carbon filament, boron filaments or the like over a shaping mold 6. Thesheets 49 are then cut to fit and sealed with any suitable sealingcompound, such as silicone rubber, to form a uniform bag 4 covering thearticle to be formed.

A flexible tube 22 is then laid periodically along the length of theformed bag 4 and sealed to the bag 4 by a circular band 58 of sealingcompound along a length of the tube 22. A tool is then inserted into thetube and both the tube and the sheet are slit 60 along a length withinthe area sealed together by the sealing compound. The tube 22 is thenconnected to a supply 23 of resin.

A vacuum is then applied around the outer edges of the molded vacuum bag4 substantially in the manner disclosed for the other embodiments above.This vacuum then draws resin from the supply tube 22, through the formedslit 60 and uniformly through the resin channels 14 formed in the sheet49, drawing the resin down uniformly, impregnating the reinforcing fibermat 2 laid over the mold 6. The pattern of channels 14 insures a uniformwetting action as well as a uniform distribution of resin.

The advantages of this embodiment are several: the sheets 49 may be massproduced for storage before use, and then fit and uniformly cut to anynumber of mold shapes, sealing the sheets together to make an overallvacuum bag 4. The bag 4 made of sheets 49 is particularly suited formultiple vacuum baggings of complex forms against a mating mold 6.

The method of applying the resin hose 22 and forming the connection fromthe resin hose 22 into the bag 4 is a particularly simple one andpermits the resin hoses 22 to be applied as flow patterns may dictatebased upon the underlying shape of the article being formed.

The inventive vacuum bag 4 of this embodiment of particular utility whenused on a vacuum table having perimeter channels for drawing a vacuumand replaceable molds for lay up of small parts which may be placed uponthe table.

It can thus be seen how this particular unitary vacuum bag 4 follows thepattern of the other embodiments in having an integrated uniform seriesof resin flow channels 14 molded within the bag 4 together a resinsupply pipe 22 molded to the bag and how the bag 4 may be easily anduniformly fit to any number of complex mold shapes for the creation of aresin impregnated fiber reinforced article.

It can thus be seen that the invention provides a vacuum bag which hasconsiderable operational advantages for repeated manufacture of fiberreinforced articles against molds, providing a unitary vacuum cover toboth seal and press the resin into the fibers, as well as providing anintegrated means for uniform distribution of resin to the fiber lay upand a uniform vacuum suction. Further the vacuum bag of the invention,being conformably build for the specific mold and article to beconstructed, has none of wrinkling and folds of the prior art planarsheets used for vacuum bags, and therefore control of the surfacesmoothness of the manufactured fiber reinforced article is improved.

The invention extends past the specific embodiments described to includethose equivalent structures and processes as will be apparent to thoseskilled in the art form the claims.

I claim:
 1. A vacuum bag assembly for use with a mold for forming afiber reinforced composite structure with a fiber lay up by vacuum bagmolding, the vacuum bag assembly comprising:a sheet having a peripheryand an inner surface, the inner surface having a contour which definesspaces between the inner surface and the fiber lay up when the innersurface of the sheet is disposed adjacent the fiber lay up, the spacesremaining present upon the application of a vacuum to evacuate air fromthe spaces and to provide for the distribution of resin between thecontoured inner surface and the fiber lay up; and a resin distributionconduit combined with the sheet so as to be removable from the compositestructure with the sheet, said resin distribution conduit in fluidcommunication with the spaces defined between the contoured innersurface and the fiber lay up.
 2. The vacuum bag of claim 1, wherein thespaces defined between the contoured inner surface and the fiber lay upcomprise passages which have a smaller cross sectional area than a crosssectional area of the resin distribution conduit.
 3. The vacuum bag ofclaim 1, wherein the contour which defines the spaces extends over mostof the fiber lay up.
 4. The vacuum bag of claim 3, wherein the spacesdefined between the contoured inner surface and the fiber lay up areV-shaped.
 5. The vacuum bag of claim 3, wherein the spaces definedbetween the contoured inner surface and the fiber lay up comprise arandom cross hatch.
 6. The vacuum bag of claim 1, wherein the contour isformed by upraised elements integrally formed in the inner surface ofthe sheet.
 7. The vacuum bag of claim 6, wherein the upraised elementscomprise a repeating pattern of bumps.
 8. The vacuum bag of claim 6,wherein the upraised elements comprise pyramidal shapes, conical shapes,spherical shapes, cylindrical shapes, oval shapes, polygonal shapes, orsquare shapes.
 9. The vacuum bag of claim 1, wherein the spaces definedbetween the contoured inner surface and the fiber lay up comprisechannels which run continuously in two cross wise directions.
 10. Thevacuum bag of claim 1, further comprising a vacuum conduit extendingaround the periphery of the sheet.
 11. The vacuum bag of claim 1,further comprising a sealant around the periphery of the sheet to sealthe vacuum bag to the mold.
 12. The vacuum bag of claim 1, wherein thesheet is formed to fit over the fiber lay up over the mold.
 13. Thevacuum bag of claim 1, wherein the sheet comprises a curable material.14. The vacuum bag of claim 1, wherein the sheet comprises an extrudablematerial.
 15. The vacuum bag of claim 1, wherein the sheet, comprises asettable material.
 16. The vacuum bag of claim 1, wherein the sheetcomprises an elastomeric material.
 17. The vacuum bag of claim 1,wherein the sheet comprises a plastic material.
 18. The vacuum bag ofclaim 1, wherein the sheet comprises a thermosetting material.
 19. Thevacuum bag of claim 1, wherein the sheet comprises a thermoplasticmaterial.
 20. The vacuum bag of claim 1, wherein the sheet comprises asilicone rubber.
 21. The vacuum bag of claim 1, wherein the sheetcomprises a polyurethane rubber.
 22. The vacuum bag of claim 1, whereinthe sheet comprises a polymer film.
 23. The vacuum bag of claim 1,wherein the sheet comprises a polyethylene material.
 24. The vacuum bagof claim 1, wherein the sheet has a stiffness sufficient to preventcollapse of the spaces against the fiber lay up under vacuum.
 25. Thevacuum bag of claim 1, further comprising a peel ply disposed betweenthe inner surface of the sheet and the fiber lay up.
 26. A vacuum bagassembly for use with a mold for forming a fiber reinforced compositestructure with a fiber lay up by vacuum bag molding, the vacuum bagassembly comprising:a sheet having a periphery and an inner surface; aresin distribution conduit combined with the sheet so as to be removablefrom the composite structure with the sheet; and a plurality of resindistribution passages integrally formed in the inner surface of thesheet, the passages in fluid communication with the conduit for resinflow from the conduit to the passages, the sheet having a stiffnesssufficient to prevent collapse of the passages against a fiber lay upunder vacuum to permit resin flow through the passages.
 27. The vacuumbag of claim 26, wherein the resin distribution passages have a smallercross sectional area than a cross sectional area of the resindistribution conduit.
 28. The vacuum bag of claim 26, wherein the resindistribution passages comprise channels separated by upraised elementsintegrally formed in the inner surface of the sheet.
 29. The vacuum bagof claim 28, wherein the upraised elements comprise a repeating patternof bumps.
 30. The vacuum bag of claim 28, wherein the upraised elementscomprise pyramidal shapes, conical shapes, spherical shapes, cylindricalshapes, oval shapes, polygonal shapes, or square shapes.
 31. The vacuumbag of claim 26, wherein the passages extend over most of the fiber layup.
 32. The vacuum bag of claim 31, wherein the passages are V-shaped.33. The vacuum bag of claim 31, wherein the passages comprise a randomcross hatch.
 34. The vacuum bag of claim 26, wherein the resindistribution passages run continuously in two cross wise directions. 35.The vacuum bag of claim 26, further comprising a vacuum conduit formedin the inner surface and extending around the periphery of the sheet.36. The vacuum bag of claim 26, further comprising a sealant around theperiphery of the sheet to seal the vacuum bag to the mold.
 37. Thevacuum bag of claim 26, wherein the sheet is formed to fit over thefiber lay up over the mold.
 38. The vacuum bag of claim 26, wherein thesheet comprises a curable material.
 39. The vacuum bag of claim 26,wherein the sheet comprises an extrudable material.
 40. The vacuum bagof claim 26, wherein the sheet comprises a settable material.
 41. Thevacuum bag of claim 26, wherein the sheet comprises an elastomericmaterial.
 42. The vacuum bag of claim 26, wherein the sheet comprises aplastic material.
 43. The vacuum bag of claim 26, wherein the sheetcomprises a thermosetting material.
 44. The vacuum bag of claim 26,wherein the sheet comprises a thermoplastic material.
 45. The vacuum bagof claim 26, wherein the sheet comprises a silicone rubber.
 46. Thevacuum bag of claim 26, wherein the sheet comprises a polyurethanerubber.
 47. The vacuum bag of claim 26, wherein the sheet comprises apolymer film.
 48. The vacuum bag of claim 26, wherein the sheetcomprises a polyethylene material.
 49. The vacuum bag of claim 26,further comprising a peel ply disposed between the inner surface of thesheet and the fiber lay up.
 50. A method of forming a fiber reinforcedcomposite structure by vacuum bag molding, the method comprising:(a)placing a fiber lay up against a mold surface; (b) providing a vacuumbag assembly comprising:a sheet having a periphery and an inner surface,the inner surface having a contour which defines spaces between theinner surface and a fiber lay up for distribution of resin when thesheet is placed over the fiber lay up, and a resin distribution conduitcombined with the sheet so as to be removable from the compositestructure with the sheet, said resin distribution conduit in fluidcommunication with the spaces defined between the contoured innersurface and the fiber lay up; (c) sealing the fiber lay up between themold surface and the vacuum bag assembly, wherein the contoured innersurface of the sheet is disposed adjacent the fiber lay up; and (d)drawing uncured resin under vacuum through the resin distributionconduit and the resin distribution spaces to impregnate the fiber layup.
 51. The method of claim 50, wherein the resin flow spaces comprisepassages which have a smaller cross sectional area than a crosssectional area of the resin distribution conduit.
 52. The method ofclaim 50, wherein the step of drawing the uncured resin under vacuumfurther comprises connecting the spaces defined by the contoured innersurface of the vacuum bag to a vacuum outlet.
 53. The method of claim50, wherein the step of drawing the uncured resin under vacuum furthercomprises providing a vacuum conduit around the periphery of the sheet.54. The method of claim 50, wherein the step of drawing the uncuredresin under vacuum further comprises connecting a source of the uncuredresin to the resin distribution conduit.
 55. The method of claim 50,further comprising curing the resin to form a composite structure. 56.The method of claim 50, further comprising allowing the resin to cure toform a composite structure.
 57. The method of claim 50, wherein the stepof sealing the fiber lay up between the mold surface and the vacuum bagfurther comprises placing a peel ply between the fiber lay up and theinner surface of the sheet.